1. Field of the Invention
The present invention relates to an apparatus and method for precisely consistently producing liquid mixtures according to a predetermined recipe, and a particular embodiment for producing slurry mixtures at the point of use for chemical mechanical polishing or planarization (CMP) processing of semiconductor wafers.
2. Background of the Invention
Much of current production CMP processing relies on mixing rather large volumes of expensive slurry in a batch preparation process somewhat remote from the point of use at a CMP workstation. The CMP processing requires many polisher workstations and hence many wafers being processed with a consistent slurry for uniform wafer results. Some slurries, particularly those including oxidizers, degrade over time. Slurry degradation results from chemical reactions that start immediately upon blending of the chemical components of the slurry. In order to maintain consistent slurries, expensive metrological instrumentation and spiking systems monitor and automatically correct mix concentrations. Often these bulk or batch slurry mixtures drift so far out of specification that restoration becomes impossible, resulting in expensive slurry waste.
More recent development has been directed to developing point of use slurry blending, or on demand blending. In U.S. Pat. No. 6,019,250, owned by the assignee of the present invention, an apparatus and method is shown for dispensing a liquid at one or more points of use from a plurality of reservoirs with a constant flow rate of liquid. This apparatus and method include a programmable logic controller for controlling valves for filling and dispensing the various liquid components to and from the reservoirs, and for controlling provision of a constant gas pressure in the reservoirs to effect the constant flow rate for the liquids. The disclosure of this patent is incorporated by reference into this application.
In another U.S. Pat. No. 5,887,974, also owned by the assignee of the present invention, a slurry mixing apparatus is disclosed using a static mixer and/or a hopper mixer in which several streams of slurry concentrate and additive chemical components are pumped together as a single stream which is blended or mixed to produce a homogeneous slurry. The disclosure of this patent is incorporated by reference into this application as well.
Other point of use slurry mixing and delivery systems are disclosed in U.S. Pat. Nos. 5,478,435 and 5,407,526. In the system of U.S. Pat. No. 5,407,526, slurry pumps preferably use a single motor to ensure the individual slurry component pumps are operated in phase for better control of the mixing of the slurry. In U.S. Pat. No. 5,478,435, the mixing of the slurry and diluting agent occurs at the point of use on the pad used in the CMP process. Liquid monitoring and control systems are used to maintain a consistent temperature and flow rate for the slurry components.
Even with such prior art on-demand or point of use slurry blending there is a desire for improved slurry consistency and greater flexibility in changing the slurry recipe during CMP wafer processing. The term slurry has a well known meaning of a mixture of liquid and finely divided particles.
There exists a general need in industry to be able to produce consistent liquid mixtures from a plurality of selected liquid components according to a predetermined recipe. It is desired that the recipe be able to be varied for flexibility of operations as well as to adjust the amounts of each liquid component not only as the desired recipe is changed, but as the characteristics of the liquid components change over time.
In accordance with the invention, a method, apparatus and system are provided for producing consistent liquid mixture according to a predetermined recipe. The apparatus comprises a plurality of liquid component reservoirs including an inlet port for loading a selected liquid component into a respective reservoir, and an outlet port through which the liquid component can be discharged. A gas manifold is provided for providing the same gas pressure within each reservoir. A plurality of valves are individually coupled to the respective outlet ports of the reservoirs. An electronic controller controls repetitive, sequences actuation of the valves to discharge precise amounts or volumes of the liquid components from the reservoirs to provide the desired liquid components as doses which are mixed together to form the liquid mixture according to the predetermined recipe.
The apparatus and method of the present invention effectuate the production of the precise, consistent liquid mixtures from the embedded electronic controller either by varying the number of actuation cycles for the valves which all have, the same actuation period, or by repetitively sequenced actuation of the valves while varying the actuation period of the valves, i.e., for normally closed valves varying the valve open periods.
In a preferred embodiment of the invention, a method, apparatus, and system are providing for producing consistent slurry mixtures to a point of use, such as a CMP polisher for semiconductor wafers. The apparatus comprises a plurality of slurry component reservoirs which include an inlet port for loading a selected slurry component into the respective reservoir, and an outlet port. Gas supply means are included to provide the same gas pressure within each reservoir. A plurality of valves, preferably having relatively high activation rates, are individually coupled to the respective outlet ports of the reservoirs. An electronic controller controls repetitive sequenced actuation of the plurality of valves to discharge upon each valve actuation precise doses of the selected components from the reservoirs to provide the desired components which are then mixed to form the predetermined consistent slurry.
The present invention also includes a system in which the apparatus of the present invention is in communication with a central operational controller which determines the selected slurry recipe which is to be blended in the apparatus for use at the point of use. The system also includes a slurry component supplier including sources of slurry components and valves via which the components fill the plurality of component reservoirs.
In a preferred embodiment, the present invention takes on-demand liquid mixing to a higher level with greater precision of resultant liquid mixture consistency and with flexibility in dynamically mixing recipes for specific CMP processing requirements. This system preferably permits varying the liquid mixture during wafer polishing and provides for rapid turn around for processing additional wafers to differing requirements.
The present invention preferably takes a different approach; mixing liquids such as slurries immediately prior to use, in the precise quantities required (for example, in the CMP embodiment, 100 to 200 ml per wafer) and allowing dynamic control of the mix recipe during wafer polishing. By utilizing relatively high frequency, rapid opening and closing valves producing many small sequential xe2x80x9cshotsxe2x80x9d or doses from each of several component reservoirs, one can achieve a precise, repeatable slurry mixing with a statistical averaging algorithm applying to numerous very small shots as well as it applies to very large batches in achieving the desired slurry mixture.
At least three different valving techniques provide the desired valve actuation cycles to achieve the statistical averaging algorithm particularly in small mixture volume applications: 1. Solenoid driven valves, 2. Stepper motor driven rotary valves and 3. Pezio electric effect driven valves may be used to provide the repetitive small dose addition of slurry components from the reservoirs to achieve the desired slurry mixture.
Pressurized component reservoirs preferably hold enough of each component to process one wafer. A recharge module quickly refills these reservoirs just prior to wafer polishing. Flow rate is controlled by maintaining the same reservoir dispense pressures coupled with hydraulic losses through the valves and static mixing elements. Each component valve xe2x80x9copensxe2x80x9d and xe2x80x9cclosesxe2x80x9d sequentially the desired number of times in each recipe segment. While, preferably, only one valve is xe2x80x9copenxe2x80x9d at any time, more than one valve can be actuated at the same time to increase the component doses supplied in a given time period. Overlapping operation of adjacent valves can ensure consistent flow rate of mixed product. The xe2x80x9copenxe2x80x9d time of each component valve varies depending on the current recipe segment requirements. Each recipe may consist of numerous segments, each segment may have a unique mix formula. Computer control enables dynamic recipe adjustment based on metrology of components (incoming chemicals), process results or product requirements. A flow sensor or scale monitors flow of the mixed product and reports flow rates at the end of each recipe segment to the host controller. The system takes configurable actions upon detection of insufficient or excessive flow rates, as defined with each recipe download. Recipes with variable flow rates are also possible.
In a preferred embodiment the design preferably supports five metered components and unmetered components although the number of components and reservoirs is a matter of choice. The mixing apparatus is integrated for operations with the CMP Polisher. The recharge components should be pressurized externally. Process nitrogen, deionized water and cleaning chemicals provide flush/purge and cleaning facility.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.